Recently in Physics and Math

What's part of the universe? You may think of it as incorporating everything that exists - both on Earth and in space - but could it also include the unknown?

In this One-Minute Physics episode, film-maker Henry Reich delves into the notion of the universe as described by physics, distinguishing between the whole universe and what's observable. He looks at the three components of the universe that we are sure of and whether mathematics could be included or not. Then there is the concept of parallel universes that could extend our understanding of space.

Time travel in the real world isn't yet possible. But thanks to new physics flicks, you can now experience an alternate universe to see what it might look like.

Developed by Wolfgang Schleich and colleagues at the University of Ulm in Germany, these first time-travel videos mathematically recreate the weird world of Gödel's universe. In the first clip, a camera is placed at the centre of this cylindrical universe, simulating what an Earth-like object would look like. Because light behaves differently in this space, as the sphere moves away from you, you see an image of both the front and the back. If it moves above you, it appears as a collection of slices. During its orbit, you see many versions from different time periods all at once.

A working tractor beam has now been caught on video, showing how light can pull objects - on a microscopic scale.

While it's well known that light can push objects as they follow the flow of photons, attracting them isn't as simple. By shining a laser through a lens and mirror set-up, Tomas Cizmar from the University of St Andrews in the UK and colleagues were able to reverse the effect, thanks to the interference pattern of reflected beams. Their technique works both in liquids and in a vacuum.

In this video, the first clip shows how the system can be used to separate objects of different sizes. When a tractor beam in the centre of a mixture of particles is turned on, large spheres move left towards the light, while smaller ones are pushed to the right.

A second clip shows how the beam can pull a collection of particles. "When the right configuration of particles occurs the tractor beam makes it stable and the whole structure moves against the tractor beam," says Cizmar.

We interact with the concept of mass every day. Without it, gravity wouldn't keep us firmly planted on Earth. But mass is also a component of inertia, making it hard, for example, to push a stalled car.

Does objective reality exist? Is there an underlying truth that doesn't depend on the observer?

According to quantum physics, there may be no consistent reality. Not only do we change the outcome of experiments by what we choose to measure, but we can alter those results after they've already happened.

In this animation, find out how our choices of what to observe can change what actually happens, and what that means for our understanding of reality. A classic experiment illustrates the conundrum by attempting to measure whether a photon behaves as a particle or a wave. It turns out that it can be either, or a mixture of both, depending on how the experiment is set up.

Even the most skilled origami practitioners would struggle with microscopic folds. But now Shoji Takeuchi of the University of Tokyo, Japan, and colleagues have created sheets that harness the traction force of cells to fold themselves into a variety of shapes.

You've probably seen a 3D movie, but what if sound could be just as immersive? Commercial surround sound systems pan audio back and forth between speakers, but physically reconstructing a sound field could produce an experience much more similar to what you hear in the real world.

You may use your kettle every day but have you ever seen what goes on inside it?
Now Sander Wildeman from the University of Twente in Enschede, the Netherlands, and colleagues have captured its inner activity to better understand the dynamics of boiling.